Reversing control system



April 6, 1954 A. c. PITMAN 2,674,710

REvERsING CONTROL SYSTEM Filed April 25, 195o P2 mM-una P2l r Annu: P41'33' l 7;/ t 5f 29 BY 37@ 8h 72\ F 74 nm/$4@ M Pz 77 .T juil 7625"@ RfATTORNEYS Patented Apr. 6, 1954 REVERSIN G CONTROL SYSTEM Arnold C.Pitman, Stamford, Conn., assigner to Electric Specialty Company, acorporation of Delaware Application April 25, 1950, Serial No. 157,958

(Cl. S18-207) 4 Claims.

This invention relates to reversing control systems and moreparticularly to a reversing control system for a single phase inductionmotor.

In conventional single phase induction motors, a main or running windingand an auxiliary or starting' winding are physically displaced from eachother on the stator of the motor and carry currents displaced in phasein order that a rotating magnetic iield be created to provide thestarting torque required to bring the motor to nearly its synchronousspeed, the phase displacement of the currents being produced in one typeof induction motor by a capacitor connected in series with the startingwinding.

In starting such motor, both windings are initially simultaneouslyenergized from a source of single phase alternating current, and whenthe motor has accelerated to a suiflciently high speed which is near thesynchronous speed thereof, the circuit to the starting winding isinterrupted and the motor runs on the main winding alone.

Such interruption of the starting winding may be, for example, by acentrifugal switch actuated by the rotor of the motor and breaking thecircuit to the starting winding when such rotor is rotating at apredetermined speed, or by a relay having a coil which may be inparallel with the starting Winding and also breaking the circuit to thestarting winding when the rotor of the motor is revolving at apredetermined speed.

In order to reverse the direction of rotation of the rotor of the singlephase induction motor, it is necessary that the phase relation of themain Winding and the starting winding be reversed. Thus, it is apparentthat the single phase induction motor cannot be reversed unless thestarting winding and running winding are both in circuit in order thatsuch phase reversal may be accomplishe-d.

Where a centrifugal switch is used to interrupt the circuit to thestarting winding and it is desired to reverse the direction of rotationof the rotor while it is running at nearly its synchronous speed, it isnecessary to disconnect the main winding from the power line so that therotor will siow down sufiiciently to permit the centrifugal switch toclose to put the starting winding back into circuit. At such time thestarting and main windings can again be connected to the power line withthe leads of either of the windings reversed irom its original positionto create a reverse torque to reverse the direction of rotation of therotor.

Such arrangement requires a considerable period of time to elapse beforethe rotor has slowed down sumciently to permit reclosure of thecentrifugal switch and as a result, rapid reversing of the rotor of themotor as by the rapid reversal of the leads of one of the windings, isnot possible, for if such reversal of the leads should occur before thestarting winding is back in circuit, the rotor will continue rotating inthe same direction.

Even where braking means are used to hasten the slowing of the motor,considerable time will elapse and the use of such braking means requiresadditional mechanical elements which add considerably to the bulk andcost of the motor and also require constant maintenance as does thecentrifugal switch used.

The relay type of circuit interrupter for the starting winding has acoil which may be in parallel with the starting winding and which isenergized to open its associated contacts to break the circuit to thestarting winding when the rotor speed has increased suiciently to inducea suiciently high voltage in the starting winding and hence in the relaycoil associated therewith to permit operation of such relay. As thestarting winding is not connected to the source of current when themotor is running at normal speed, if the leads to the main windingshould be reversed, no reverse torque would be developed as both themain and starting windings must be in circuit for this to occur. Henceno reversal of the direction of rotation of the rotor would take placeas the alternating current through the main winding would still drivethe rotor and the rotor would still induce a voltage in the startingwinding and hence in the relay coil associated therewith to maintain thelatter energized. Thus the contacts of the relay will remain open sothat no current would be applied from the main power line to thestarting winding and hence no relative phase reversal between thestarting winding and running winding would be effected, which isnecessary for the reversal of the motor.

It is accordingly among the objects of the invention to provide areversing control system for single phase induction motors of thecapacitor type, using but few conventional relatively inexpensive partswhich are not likely to become out of order and hence require little orno maintenance and by the use of which, upon the closing of a switch,even when the motor is running at nearly synchronous speed, reversetorque may be instantly developed without need for centrifugal switches,brakes or complicated circuits.

Another object of the invention is to provide a single phase inductionmotor with a reversing vcontrol system of the above type whichnevertheless, will automatically and without need for opening andclosing of the main power line switch, resume synchronous speed in thedirection of its rotation upon relief of an overload that hastemporarily slowed it down.

Another object is to provide a reversing control system of the abovetype for single phase induction motors adapted for use With twodifferent input voltages.

According to one aspect of the invention, the reversing control systemfor the single phase induction motor of the capacitor type, includes aof relays each having a pair of normally closed contacts and a coilassociated with the starting winding of the motor. Switch means areprovided, associated with such relays so that either one or the other ofthe coils thereof may be put into circuit with such starting winding.Circuit means associated with the switch provide a path from a source ofcurrent, through said switch to said main winding, and also from saidsource of current through said switch and through one or the other ofsaid pairs of normally closed contacts to said starting winding. rfheswitch is so arranged that the phase of the input voltage to thestarting winding with respect to the phase of the input voltage to themain winding will be reversed 180 as one or the other of the pair ofnormally closed contacts is put in circuit with said starting winding toreverse the direction of rotation of the rotor of the motor. Additionalcircuit means are also provided associated with said switch so that inone position of the latter, when the coil of one of the relays is incircuit with the starting wind ing, the coil oi the other relay will beshorteircuited, thereby retaining closed the contacts associated withsaid short-circuited coil to provide a closed circuit from said firstcoil to said starting winding. Thus upon attaining by the rotor of saidmotor of nearly synchronous speed the increased voltage in said startingwinding will be transmitted to said coil in circuit therewith toenergize said coil, thereby opening the contacts associated therewith tobreak the circuit.

In a specific application of the invention, the coils of one or theother of the relays may be placed in parallel with the starting windingand the pair of contacts associated with the coil in parallel with saidstarting winding will be in series with the latter and with the sourceof current, and the pair of contacts of the other coil will be in serieswith the first named coil..

According to another aspect of the invention, the main winding of themotor has two sections and switch means are provided in circuit withsaid sections to connect the latter in series or in parallel as desired.

In the accompanying drawings, in which are shown one or more of variouspossible embodiments of the several features of the invention,

Fig. 1 is a circuit diagram of one embodiment or the control system,

Fig. 2 is a view similar to Fig. 1 of another embodiment of the controlsystem, and

Fig. 3 is a circuit diagram of the switching arrangement to adapt themain winding for use with two different input voltages.

Referring now to the drawings, in Fig. 1 is diagrammatically shown asingle phase induction motor M having a main or running winding II andauxiliary or starting winding I2 physically displaced from the mainwinding, and a rotor I3 driven by said windings. The necessary phaseydisplacement between the currents in the main and starting windings IIand I2 necessary to produce the rotating field required to revolve therotor I3, is provided by means of the capac:. tor 14 which is desirablyconnected in series with the starting winding I2 during starting of themotor, in the manner hereinafter to be described. As such capacitor typesingle phase induction motor is conventional in construction, it wilinot be further described.

The control system for such motor l/l desirably comprises a conventionaldouble throw, triple pole switch I5 and a pair of conventional relays I6and I 'I, each desirably having a coil Iii and I9 respectively, and axed contact ZI, 22 respectively and a movable contact 223, 26 normallyengaging said fixed contacts 2l, 22 respectively.

The movable switch arms 25, 2E and 2? of switch I5 are ganged, desirablyby an insulating member 28, and switch arm 25 is connes f lead 29 to oneside P1 of the source of alt ing current, the poles 3I and 32 associatedwith said switch arm 25 being electrically connected by lead 33. Pole 3|is connected by lead 34 to one side of the main winding II of motor M,the other side of said winding II being connected by lead 35 to commonjunction 36 which is connected by lead 3'! to the other side P1. of thesource of alternating current.

Junction 36 is also connected by lead 38 to movable switch arm 2B ofswitch I5 and by lead 39 to one side of the coil I8 of relay I6. riheother side of said coil I8 is connected by leads 4I, d2 to movablecontact 24 of relay Ii and by leads 4I, 43 to pole 44 associated withmovable switch arm 26 of switch I5. Pole 45 or said switch I5 alsoassociated with movable switch arm 26, is connected by lead 4B to poleIl of said switch I5 and by lead 48 to one side of the starting windingI2 of motor M, the other side of said. starting winding I2 beingconnected by leads 49 and 50 to the fixed contact 2l oi relay i6 andalso by lead 5I to the xed contact Z2 oi' relay Il. The movable contact23 of relay IB is connected by leads 52 and 53 to pole 54 of switch I5associated with movable switch arm 21 and by lead 55 to one side of thecoil I5 oi. reiay Il. The other side of said coil I9 is connected byleads 56 and 51 to the movable sw ch arm 21 and by leads 56 and 58 toone side of capacitor I4, the other side of said capacitor being comnected by lead 59 to pole 32.

Ii desired, a running capacitor 61 may be con nected by leads 62 and 53respectively, to xed contact 22 of relay I1 and to pole 32 orf switchi5.

In the operation of the control system with the movable contact arms ofswitch I5 in the position shown in full lines in Fig. l, as movablecontact arm 25, which is connected by lead 23 from one side P1 of thepower line, is not engaging either of the poles 3| or 32 associatedtherewith, the circuit will be open and hence the starting and mainwindings will not be energized and either of the relay coils I8 and I9will be energized.

To start the motor it is merely necessary to throw the switch so thatthe movable switch arms thereof are, for example, in the position shownin dot and dash lines in Fig. 1. In this position, a circuit will becompleted to both the main and starting windings I I and I2 and to thecoil I8 of relay I6. This circuit is from main Pi through lead 29 tomovable switch arm 25 which engages pole 3|, thence through lead 34,main winding I I, lead 35 to junction 3B, thence by lead 31 to powerline P2. Thus, the main winding will be energized. The circuit; to thestarting winding is from main P1, lead 29, movable switch arm 25 whichis engaging pole 3i, lead 33 to pole 32, thence through lead 59 to onesideof capacitor I4 and by leads 58 and 51 to movable switch arm 21which is engaging pole 54. Lead 53 connected to pole 54 goes by way cflead 52 to movable contact 23 of relay I6 which is normally engagingfixed contact 2|, the latter being connected by leads 59 and 49 to oneside of starting winding l2. The other side of the starting winding I2is connected by lead 48 to pole 45 which is engaged by movable switcharm 26, the latter being connected by `lead 38 to junction 36 which inturn is connected by lead 31 to the other side of the power main P2. i

By reason of the capacitor I4, a 90 phase displacement will be eiiectedbetween the voltage applied to the main starting windings II and I2thereby creating the rotating iield necessary to start the rotation ofrotor I3.

The coil I9 of relay I5 is connected in circuit with the startingwinding I2 desirably in parallel as shown as follows: From pole 45 towhich lead 43 from the starting winding I2 is connected, through movableswitch arm 26, leads 38 and 39, tol one side of coil i8 and from theother side of the coil through leads 4I and 42 to the movable contact 24of relay I1 which normally engages fixed contact 22, the latter beingconnected by leads 5I and 49 to the other side of the starting windingI2.

It is to be noted that the coil oi relay I1 will be short-circuited andhence de-energized when the coil I8 of relay I5 is in circuit, therebyto retain contacts 22, 24 in engagement to provide a closed circuit forthe coil I8 of relay IB. The short circuit path for the coil I9 of relayi1 is as follows: From one side of the coil I9 of relay I1 through lead56 to point X and from the other side of the coil I9 through leads 55and 53 to pole 54 engaged by movable switch arm 21 and thence by lead 51to point X.

Although coil I8 is thus connected in parallel with starting winding I2,insuiicient voltage is initially developed across such coil and hencethe contacts 2I and 23 associated therewith remain in engagement. As therotor accelerates, the

voltage across the starting winding I2 will increase as will the voltageacross coil I8. When the voltage across coil i8 has increased to apredetermined amount which will occur when the rotor has attained nearlyits synchronous speed,

the coil will be energized sufficiently to attract movable contact 23and separate the contents 2| 23 thereby breaking the circuit from thepower line P1 to the starting winding I2.

This is the condition which is desirable in single phase inductionmotors, for if the starting winding I2 and its associated capacitor I4remained in circuit during the normal running of the motor, considerablecurrent would be drawn with the resultant development of excess heat andconsequent low efciency and possible burning out of such startingwinding I2. By reason of the fact that the revolving rotor I3 willinduce a voltage in the adjacent starting winding I2, which voltage willbe impressed across the coil I8 of relay I6 in parallel therewith and asthis voltage will be suiiicient to keep such coil energized, thecontents 2l and 23 will remain open, thereby keeping the startingwinding l2 disconnected from the power line P1, and the motor willthereafter run on the main winding Il in conventional manner.

When it is desired to reverse the direction of the rotation of the rotorI3 of the motor, the polarity of one of the windings must be reversedwith respect to the polarity of the other winding, thereby developing areverse torque which will cause the rotor to come to a standstill andthereupon start turning in a direction opposite to the one in which ithad previously been rotating.

It is apparent that for such reverse torque to be developed both themain winding li and the starting winding I2 must be in circuit at thesame time. However, when the motor rotor had attained its normal runningspeed, as previously described, the circuit of the starting winding l2to the power main P1 had been interrupted by the open contacts 2l and23, which are retained in such open position during the running of themotor at normal speed, by the energization of coil I8 in parallel withthe starting winding I2.

It is apparent, therefore, that in order for there to be instantaneousapplication of reverse torque to cause reversal of direction oi rotationof the rotor I3 upon throwing switch I5, it is necessary that means beprovided instantly to close the circuit to the starting winding from themain P1 and that the polarity of the voltage ape plied to one of thewindings be reversed. To this end it is merely necessary to move themovable switch arms of switch I5 to the right to the position shown indashes in Fig. 1. In this position a circuit will be completed to boththe main and starting windings II and I2 and to the coil I9 of relay I1and the polarity of the voltage applied to the starting winding I2 withrespect to the voltage applied to the main winding I I will be reversed.This circuit will be from power line P1 through lead 29 to movableswitch arm 25 which engages pole 32, thence through lead 33 to pole 3land from pole 3l through lead 34 to one side of main winding II, andfrom the other side of main winding II through lead 35 to junction 35,thence by lead 31 to power line P2. Thus, the main winding Il will beenergized. The circuit to the starting winding is from power line Pi,lead 29 to movable switch arm 25 which engages pole 32, thence by lead59 to one side of capacitor I4 and from the other side of capacitor I4by leads 58 and 51 to movable switch arm 21 which engages pole 41.Thence by lead 46 connected from pole 41 to pole 45 and by lead 43 toone side of starting winding I2 and thence from the other side of thestarting winding i2 through leads 49v and 5I to fixed contact 22 ofrelay I1 which is normally engaged by movable contact 24. Thence byleads 42 and 43 to pole 44 which is engaged by movable switch arm 23 andby lead 38 from said switch arm 2S to junction 35 which is connected bylead 31 to the other side of the power line P2.

With the circuit thus connected it is apparent that the polarity of thevoltage applied to the Starting winding I2 with respect to that appliedto the main winding II has been reversed from that previously applied asheretofore described.

As a result, with the movable switch arms of switch I5 in the positionshown in dashes in Fig. l, a reverse torque will be developed whichwill. immediately slow down the motor until the rotor I3 thereof is at astandstill and thereupon by reason of the fact that a 90 phasedisplacement will be effected by the capacitor I4 between the voltagefed to the main and starting windings II and l2 respectively, therotating eld created will turn the rotor I3 in the opposite direction tothat which it had been previously turning.

With the switch I in the position shown in dashes in Fig. l, the coil I9of relay I1 is connected in parallel with the starting winding I2.

The circuit is from one side of coil I9 through leads 55 and 51 tomovable switch arm 21 which engages pole 41, thence by lead 46 to pole45 which is connected by lead 49 to one side of the starting winding I2,thence from the other side of the starting winding through leads 49 and50 to fixed contact 2I of relay I6 normally engaged by movable contact23. Thence by leads .52 and 55 to the other side of coil I9.

It is to be noted that the coil IB of relay I6 will be short-circuitedand hence de-energized when the coil of relay I1 is in circuit to retaincontacts 2 I, 23 in engagement to provide a closed circuit for the coilI9 of relay I1. The short-circuit path for the coil I8 of relay I6 is asfollows: From one side of the coil I8 through lead ill to the point Y,and from the other side of the coil I8 through lead 39 to junction 36,and thence by lead 38 to movable switch arm 26 which is engaging pole 44and by lead 43 to point Y.

As the operation of the motor with the switch in the position shown indashes in Fig. 1 is substantially the same as when the switch I5 is in.the position shown in dot and dash lines in 1, it will not be described.

It is apparent from the above description that when the switch is movedto either the position shown in dot and dash lines or the position shownin dashes in Fig. l, the starting Winding I2 will immediately be put incircuit and the polarity of the voltage in the starting winding withrespect to the polarity of the voltage in the main winding will alsoimmediately be reversed Thus, with the circuit above described with theuse of a conventional self-starting single phase induction motor and aconventional -pole double-throw switch and conventional relays, it ispossible quickly to move the switch I5 from one position to the otherimmediately to develop a reverse torque on the rotor I3 that will causereversal in the direction of rotation thereof without the need for ilrstinterrupting the circuit from the power line to the main and startingwindings II and I2 and thereupon allowing the motor to slow down almostto a standstill before re-closing the circuit to the windings I I andI2. As such latter procedure is time-consuming, it is not desirable forindustrial application where it essential that reversal be effected bythe mere rapid throwing of a switch.

addition, the above circuit dispenses with a need for centrifugalswitches to open the circuit to the starting winding and of brakes toslow i down the speed of the rotor so that it can be more quicklyreversed. Such centrifugal switches and. brakes are undesirable as theyadd materially to the bulk and cost of the system and in addition asthey have many parts that are likely to wear and break down, they addgreatly to the maintenance cost and idle time of the motor.

With the system above described, in the event that a sudden overloadshould be applied to the motor while it is running, which would slow itdown or perhaps stop the motor, upon removal of such overload, one ofthe relays I5 or I1 as the case may be, would always be in parallel withthe starting winding, and the contacts` of such relay would close whenthe speed of rotation of the rotor I3 had decreased sufficiently tocause the voltage induced in the starting winding and hence in the coilof the associated relay to fall below a certain amount. Closure of suchcontacts would again close the circuit from the power line P1 to thestarting winding so that a rotating field would again be provided tocause the rotor of the motor to resume its normal speed.

Thus the system above described dispenses with the need for opening thepower line circuit after the overload has been removed and again closingsuch circuit to put the main and starting windings back into the powerline circuit.

Although the switch I5 has been shown as a 3-pole double-throw switch,it is of course understood that other switching arrangements could beused for the same purpose. Thus, a separate switch could be provided forthe power line and a separate reversing switch could be provided, or apush button could be used to actuate a relay that operated the switch.As such switching arrangement would lbe obvious in view of thedisclosure herein, it will not be further described.

It is also to be noted that when the switch I5 is in the intermediateposition as shown in full lines in the drawings, the motor will be at astandstill with both the main and starting windings disconnected fromthe source of current Pi, Pz.

Although the circuit above described has been shown incorporated with asingle phase induction motor adapted for use with a single given inputvoltage, it is a relatively simple matter to modify the main winding ofthe motor so that it may be used for two voltages, i. e. for volts or220 volts. To this end the circuit shown in Fig. 2 is provided.

As can be seen, this circuit is substantially identical to the circuitof Fig. l with substantially the only difference in the two circuitsbeing in the construction of the main winding and the manner ofconnecting such main winding to the source of current. Consequently,parts shown in Fig. 2 corresponding to those shown in Fig. l have thesame reference numerals primed.

As shown in Fig. 2, the main Winding II is split into two separatewindings IIa and IIb. One end of each of the windings are connectedtogether by leads 66 and 61 to a common point Z which is connected bylead 61 to junction 3B and thence by lead 38 to movable switch arm 26and by lead 39 to one side of the coil I8 of relay I6. The free end ofwinding IIa connected by lead 34 to pole 3i and the free end of windingIIb is connected by lead 31 to one side of the power line P2'.

Thus, windings II a and IIb are in series with each other which is thecondition in which they must be for 220 volt input.

In order to connect the windings for 110 volt input, it is merelynecessary to connect windings IIa and IIb in parallel.

To this end, as shown in Fig. 3, a switch 10 may be provided desirablyhaving at least three contacts, 1I. 12 and 13 and a movable insulatingmember 14 desirably carrying a pair of contact arms 15 and 16. In oneposition of the switch, arm 15 will be spaced from its associatedcontact 1I and arm 16 will engage its associated contact 12 and in theother position of the switch, arm 15 will engage contact 1I and arm 16will engage contact 13.

The power main P1' is connected by lead 29 to movable switch arm 25 andpower main P2 is connected by leads 11 and 18 to contact 13 and by leads11 and 31 to one side of the winding IIb, the other side of said windingbeing connected by lead 19 to contact 1I and by lea/:l 8l to contact 12.Arm 16 is connected by lead 83 to one side of the winding Ha and byleads 83 and 38 to movable switch arm 25', the other side of winding liabeing connected by lead 34 to pole 3i and by leads 's3-i and d5 to arm lof switch lil.

Thus, when the switch. is in the position shown in Fig. 3 with arm 'i5spaced from contact ll and ann l5 engaging contact l2, windings lla andHb will be in series and the main winding I l is set for an input or 220volts and when arm 'I5 is engaging contact li and arm it? is engagingcontact T3, the windings I la and lib will be in parallel set for aninput of llo volts.

As many changes could be made in the above construction, and manyapparently widely different embodiments of this invention could be madewithout departing from the scope of the claims, it is intended that allmatter contained in the above description or shown in the accompanyingdrawings shall be interpreted as illustrative and not in a limitingsense.

Having thus described my invention, what l claim as new and desir@ tosecure by Letters Patent of the United States is:

1. A reversing control system for a single phase induction motor of thetype having a stator including a main winding and a starting winding and`a rotor, said control system comprising means for connecting saidwindings to a source of current to eect rotation of said rotor, a pairof relays each having a coil and a pair oi normally closed contacts,means to connect the coil of one of said relays in parallel with saidstarting winding, means to connect the contacts oi said parallelconnected relay in series with said starting winding, means toshort-circuit the coil of the otherof said relays, means to connect thecontacts of said second relay in series with the coil of saidfirst-named relay and with said starting winding, means to reverse thepolarity of the current applied to one ci said windings with respect tothe other, said last named means including means to short-circuit thecoil oi said iirst relay and to connect its contacts in series with thecoil of said second relay and with said starting windings, and means toconnect the coil of said second relay in parallel with said startingwinding with its contacts in series with said starting winding and thesource of current.

2. A reversing control system for a single phase induction mot-or of thetype having a stator including a main winding and a starting winding anda rotor, said control system comprising switch means for connecting saidwindings to a source of current to effect rotation of said rotor, meansindependent of said switch means for opening the circuit from suchsource of current to said starting winding after said rotor has exceededa predetermined speed, said means including a iirst relay and a secondrelay each having a coil and a pair of normally closed contacts, saidswitch means including means for connecting the coil of said rst relayin parallel with said starting winding, means for connecting the pair ofcontacts of said first relay in series with said starting winding, meansto shortcircuit the coil of said second relay, and means to connect thepair of contacts of said second relay in series with the coil of saidi'lrst relay said starting winding, said switch means including means toreverse the polarity of one of said windings with respect to the otherof said windings, means to short-circuit the coil of said rst relay andconnect its contacts in series with the coil of said second relay andwith said starting winding and means to connect the coil of said secondrelay in parallel with said starting winding with its contacts in serieswith said starting winding, said relay coils when in circuit beingadapted to be energized when said motor is running at substantiallynormal speed to open the pair of normally closed contacts associatedtherewith to break; the circuit from the source of current to saidstarting winding, said coil in circuit remaining energized due to thecurrent induced in said starting winding by said rotor.

3. The combination set forth in claim 2 in which said main winding hastwo sections and manually operated switch means are provided to connectsaid sections at will, in parallel across such source of current or inseries across such source of current.

4. A reversing control system for an induction motor of the type havinga main winding, a starting winding and a rotor, said control systemincluding a pair of rela-ys each having a coil and a pairof contacts,and switch means comprising three movable switch arms each having a pairof associated contacts, leads connecting one side of said main windingto one side o the coil of one or said relays and to the switch armassociated with one of said pairs of switch contacts, a lead connectingone of the contacts of said last named pair of switch contacts to oneside of said starting winding, a phase displacement device, a leadconnecting one side of said phase displacement device to one oi thecontacts of said second pair of switch contacts, a lead connecting theother side of said main winding tc the other of the contacts ci saidsecond pair of switch contacts, a lead connecting said second named pairof switch contacts, a lead connecting the other side of said startingwinding to one of the contacts ci each of said relays, a lead connectingthe other side of the coil of said irst-named relay to they othercontact of said second-named relay and to the other contact of saidfirst-named pair of switch contacts, a lead connecting one of thecontacts of said thirdnamed pair of switch contacts to the other contactof said first-named relay and to one side oi the coil of saidsecond-named relay, a lead connectirrg the other contact of saidthird-named pair of switch contacts to the contact oi said rst-namedpair of switch contacts to which one side of the starting winding isconnected, a lead connecting the other side of said last-named coil tothe movable switch arm of said third-named pair of switch contacts andto the other side of said phase displacement device, and means forconnecting a source of current to the switch arm associated with saidfirst-named pair of contacts and to the switch arm associated with saidsecond-named pair of switch contacts.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,024,726 Ehrenfeld Dec. 17, 1935 2,100,425 Berger et al Nov.30, 1937 2,195,287 Schaefer Mar. 26, 1940 2,280,388 Buchanan Apr. 28,1942 2,388,332` Brongersma Nov. 6, 1945 2,447,675 Walley Aug. 24, 19482,473,244 Fuller June 14, 1949 2,509,898 Wiseman May 30, 1950 2,545,639Wolff Mar. 20, 1951

